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From: Nathan Chancellor <natechancellor@gmail.com>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Hanjun Guo <guohanjun@huawei.com>,
	Sudeep Holla <sudeep.holla@arm.com>, Jens Axboe <axboe@kernel.dk>,
	Joerg Roedel <joro@8bytes.org>, Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Christoph Hellwig <hch@lst.de>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-ide@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Paul Burton <paulburton@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	x86@kernel.org, linux-acpi@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>, James Hogan <jhogan@kernel.org>,
	Len Brown <lenb@kernel.org>,
	devicetree@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	linux-mips@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
	iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2] dma-mapping: treat dev->bus_dma_mask as a DMA limit
Date: Sat, 23 Nov 2019 09:51:08 -0700
Message-ID: <20191123165108.GA15306@ubuntu-x2-xlarge-x86> (raw)
In-Reply-To: <20191121092646.8449-1-nsaenzjulienne@suse.de>

On Thu, Nov 21, 2019 at 10:26:44AM +0100, Nicolas Saenz Julienne wrote:
> Using a mask to represent bus DMA constraints has a set of limitations.
> The biggest one being it can only hold a power of two (minus one). The
> DMA mapping code is already aware of this and treats dev->bus_dma_mask
> as a limit. This quirk is already used by some architectures although
> still rare.
> 
> With the introduction of the Raspberry Pi 4 we've found a new contender
> for the use of bus DMA limits, as its PCIe bus can only address the
> lower 3GB of memory (of a total of 4GB). This is impossible to represent
> with a mask. To make things worse the device-tree code rounds non power
> of two bus DMA limits to the next power of two, which is unacceptable in
> this case.
> 
> In the light of this, rename dev->bus_dma_mask to dev->bus_dma_limit all
> over the tree and treat it as such. Note that dev->bus_dma_limit should
> contain the higher accesible DMA address.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
<snip>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 041066f3ec99..0cc702a70a96 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -421,8 +421,7 @@ static dma_addr_t iommu_dma_alloc_iova(struct iommu_domain *domain,
>  	if (iova_len < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1)))
>  		iova_len = roundup_pow_of_two(iova_len);
>  
> -	if (dev->bus_dma_mask)
> -		dma_limit &= dev->bus_dma_mask;
> +	dma_limit = min_not_zero(dma_limit, dev->bus_dma_limit);
>  
>  	if (domain->geometry.force_aperture)
>  		dma_limit = min(dma_limit, domain->geometry.aperture_end);

Just as an FYI, this introduces a warning on arm32 allyesconfig for me:

In file included from ../include/linux/list.h:9,
                 from ../include/linux/kobject.h:19,
                 from ../include/linux/of.h:17,
                 from ../include/linux/irqdomain.h:35,
                 from ../include/linux/acpi.h:13,
                 from ../include/linux/acpi_iort.h:10,
                 from ../drivers/iommu/dma-iommu.c:11:
../drivers/iommu/dma-iommu.c: In function 'iommu_dma_alloc_iova':
../include/linux/kernel.h:851:29: warning: comparison of distinct pointer types lacks a cast
  851 |   (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
      |                             ^~
../include/linux/kernel.h:865:4: note: in expansion of macro '__typecheck'
  865 |   (__typecheck(x, y) && __no_side_effects(x, y))
      |    ^~~~~~~~~~~
../include/linux/kernel.h:875:24: note: in expansion of macro '__safe_cmp'
  875 |  __builtin_choose_expr(__safe_cmp(x, y), \
      |                        ^~~~~~~~~~
../include/linux/kernel.h:884:19: note: in expansion of macro '__careful_cmp'
  884 | #define min(x, y) __careful_cmp(x, y, <)
      |                   ^~~~~~~~~~~~~
../include/linux/kernel.h:917:39: note: in expansion of macro 'min'
  917 |  __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
      |                                       ^~~
../drivers/iommu/dma-iommu.c:424:14: note: in expansion of macro 'min_not_zero'
  424 |  dma_limit = min_not_zero(dma_limit, dev->bus_dma_limit);
      |              ^~~~~~~~~~~~

Cheers,
Nathan

  parent reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-21  9:26 Nicolas Saenz Julienne
2019-11-21 15:24 ` Christoph Hellwig
2019-11-21 15:26   ` Nicolas Saenz Julienne
2019-11-21 15:26   ` Christoph Hellwig
2019-11-21 15:55     ` Robin Murphy
2019-11-21 16:02       ` Christoph Hellwig
2019-11-21 16:53         ` Will Deacon
2019-11-21 17:16           ` Christoph Hellwig
2019-11-21 17:07 ` Robin Murphy
2019-11-21 17:17   ` Christoph Hellwig
2019-11-23 16:51 ` Nathan Chancellor [this message]
2019-11-25  7:44   ` Christoph Hellwig
2019-11-25 16:33     ` Robin Murphy
2019-11-26 18:51       ` Nicolas Saenz Julienne
2019-11-26 21:45         ` Robin Murphy

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